A dearth of information about the ingredients of various oil-dispersing formulas is complicating an increasingly rancorous debate over which, if any, is the best choice for cleaning up the catastrophic spill in the Gulf of Mexico.

As the quantity of dispersant that BP has sprayed on the spill surpassed 800,000 gallons last weekend, experts say the secret formulas, combined with the sparse water-quality data released by U.S. EPA, make an independent assessment of the dispersant strategy next to impossible.

Some scientists are calling for all dispersant use to be halted until the ingredients and effects are better understood.

"The data is horrible," said Carys Mitchelmore, an environmental chemist and toxicologist at the University of Maryland's Center for Environmental Science. A co-author of a 2005 National Academy of Sciences report on dispersants, she has testified repeatedly on Capitol Hill over the gaping holes in the scientific knowledge regarding the chemicals.

"There's two frustrations," Mitchelmore said. "One, I don't know what's in them, and secondly, I really hope they are running toxicity tests with all of these right now to get a more robust scientific data set."

The company responsible for containing the spill, BP PLC, continued to spar with EPA over the company's decision to rely on two types of Corexit -- proprietary dispersant formulas manufactured by Nalco Holding Co., which has close ties to both BP and Exxon Mobil Corp.

EPA's own data indicate that Corexit may not be the least toxic or most effective option available, and last week, the agency ordered the company to switch to something less toxic within 24 hours.

On Saturday, BP rejected the order, citing an ingredient in a potential alternative formula, called Sea Brat #4, that could degrade into a nonylphenol, a class of chemicals believed to be disruptive to hormone systems.

BP's letter and accompanying analysis, which included numerous redactions, also said the company was unable to identify ingredients in other proprietary oil dispersants, concluding that Corexit remained the safest and most abundant option available.

"We're still using it because, as of today, it's still the best product available," said Doug Suttles, chief operating officer for BP, on CNN today. "It is on the approved list. It is safe to use. It is the most widely used."

Suttles said BP would continue to consult with EPA to determine whether to switch from Corexit. An EPA spokesman said the agency had not yet publicly responded to BP's decision.

"We're going to continue to study this with the EPA," Suttles said. "We're going to work with them every single day. We've met again last night with them; if there is a better product that's available, we'll use it."

Scientists, meanwhile, are stepping up their questions and criticisms concerning the use of dispersants, noting that the vast quantities being used to ensure the oil sinks into the ocean rather than washing up on beaches and coastal wetlands could wreak long-term havoc on the marine environment and ultimately complicate cleanup.

EPA Administrator Lisa Jackson has called the decision to allow BP to use dispersants a "trade off" between risking harm to a portion of the ocean and protecting the coast from a thick oil slick that could linger on shorelines for decades.

Calls for halting dispersant use

On Capitol Hill, two ocean experts told a House panel Friday that the use of the oil-dispersing chemicals should be halted until the ingredients and effects are better understood.

"Until we know more about the dispersants, I'd follow up with BP and EPA and tell them to stop, stop," legendary oceanographer Sylvia Earle told the Energy and Commerce Committee.

"It's not at all clear to me why we're dispersing the oil at all," said Carl Safina, president and co-founder of the Blue Ocean Institute. "It seems to me you would want it as thick and as concentrated so we can deal with it right there. We seem to be saying we're going to take this concentrated oil, and we're going to dissolve it. It's an out-of-sight, out-of-mind strategy. It's a PR stunt to dissolve this oil with dispersants. It's just to get it out of the way of the cameras on the shoreline."

Others criticized BP's written response for its redactions, saying the marked-out portions of the letter represented clear defiance of the Obama administration's calls for transparency.

"The administration demanded transparency from BP, and we got censored documents," said Jeremy Symons, the National Wildlife Federation's senior vice president. "BP cannot be trusted, and this is not acceptable. These toxic chemicals have been dumped in the Gulf for a month at levels never envisioned, and any information that sheds light on their effects and the potential for less toxic dispersants needs to be made public immediately."

Also on Friday, the National Science Foundation awarded a rapid-response grant to scientist David Valentine of the University of California, Santa Barbara, and colleagues to study how the use of dispersants will affect the ability of microbes to break down the oil.